In the figure below, how many more smiley faces must be added to make the ratio of the number of smiley faces to the total number of shapes become 2 : 3?

1. Find the new ratio of smiley faces to hearts

The new ratio of smiley faces to total shapes is $2 : 3$.
Therefore, the new ratio of smiley faces to hearts is $2 : (3 - 2) = 2 : 1$.

2. Calculate the required number of smiley faces

The number of hearts remains unchanged at $4$.
Required number of smiley faces $= 4 \times 2 = 8$.

3. Find the number of smiley faces to add

Current number of smiley faces $= 5$.
Number of smiley faces to add $= 8 - 5 = 3$.